This present invention relates to the general area of turboprop engines. More particularly, it concerns feathering the fan blades of a turboprop engine.
In a manner that is known, a turboprop engine includes at least one set of fan blades that is driven in rotation by a turbine rotor. These fan blades have the particular feature of being of the variable-pitch type, meaning that their angular orientation can be altered in order to optimally control the thrust of the turboprop engine and the speed of rotation of the propellers. To this end, the mechanisms to control the orientation of the fan blades generally include a hydraulic actuator that is coupled to the blades and in which the position of the rod on the movement trajectory of the actuator determines the angular orientation of the blades.
In addition, on a turboprop engine, in the event of failure of the turboprop engine and/or of the control mechanism for orientation of the fan blades, it is necessary, for safety reasons, to align the blades of the turboprop engine in the direction of the air flow so as to limit drag. We also speak of feathering or putting the blades into minimum incidence position.
Feathering of the blades of a turboprop engine is generally performed by a device that is independent of the control mechanism for orientation of the fan blades, and that is used to force the blades to align themselves in the direction of the airflow. Such a device is usually composed of an individual hydraulic circuit, that is with its own pump and its own control, which operates the actuator of the control mechanism for orientation of the blades up to the travel limit stop of the latter, where this travel limit stop corresponds to feathering of the blades. A feathering device of this type is particularly complex to create however, is not very reliable, and is difficult to incorporate into a two-propeller aircraft turboprop engine. Apart from this, such a mechanism cannot be used to feather the blades in the event of failure of the actuator (in fact, it is precisely the actuator that operates the blades in order to feather them).